Atmospheric Charge Redistribution

Before, during, and after lightning strikes to ground, highly mobile
charged cloud centers redistribute themselves, attempting to reach equilibrium
with opposing polarity earth charges, including man-made (conductive)
structures. This atmospheric charge redistribution (ACR) creates strong
electromagnetic fields similar to those of lightning. ACR can deliver
voltage and current surges into conductors similar to those caused by
cloud-to-ground lightning.

Example: ACR charges may be imposed upon parts of a building.
Differing magnitudes of charge (di/dt) then are a function of the buildings
various metallic systems (e.g., buried cast iron water lines, overhead
power lines, adjacent connected radio towers, roof-mounted service equipment).
Charge differentials can occur due to faster buildup or reduction in
one nearby conductor than in another. When the dielectric breakdown
of the air between the two sources is exceeded, a localized arc can
occur. Resulting damage can range from data corruption to physical equipment
failure. Yet there may have been no observed lightning. Proper attention
to bonding and surge protection can ameliorate this problem.